1. Field of the Invention
The invention relates to novel foam glass compositions and method for making the same based on diatomaceous earth, fly ash or mixtures thereof. As a result of the decreasing availability of energy sources, there has been a growing demand for heat insulating and acoustic materials capable of withstanding diverse conditions, and which have low thermal conductivity, high strength, chemical resistance, low water absorption, fire resistance, high temperature resistance, rot resistance, and termite resistance.
The well-known insulating materials such as glass fiber, polystyrene and polyurethane have found widespread acceptance, but lack structural strength, and are not resistant to high temperature conditions. In the case of polystyrene and polyurethane, toxic fumes are generated when they burn.
Foam glass can be substituted for asbestos, which has been virtually abandoned as an insulation material due to health hazards associated with its use. Foam glass can be made in various shapes and configurations for use in the construction industry, and can be utilized as a substitute for wooden boards, planks, sheets, shingles, and acoustic tiles.
2. Description of the Prior Art
Foam glass has long been known as a potential substitute for conventional insulation and acoustic materials for the building industry. Foam glass is essentially a glass or glass-like composition which has been rendered highly porous by the addition of gasifiers or foaming agents, which liberate gas or vapor when the glass is melted. The publication, Demidevich, Manufacture and Uses of Foam Glass, National Technical Information Service, Publication No. AD/A-05 819, discloses foam glass compositions and methods for making foam glass utilized throughout the world up through 1972. The most common technique for making foam glass on a commercial scale involves the melting of a window-type glass composition followed by fritting and grinding, in a continuous action ball mill while adding gasifiers. The ground glass containing gasifiers is placed in a heat-resistant mold lined with a refractory material to prevent sticking. Foaming is carried out in tunnel furnaces equipped with roller conveyors followed by annealing of the foamed blocks in a separate furnace for thirty (30) hours. This commercial process suffers from the drawback that the annealing process requires a large space and long annealing times, which is not economical.
Another method for making a foam glass is disclosed in U.S. Pat. No. 3,592,619 to Elmer et al, which is directed to making a high-silica glass foam from a borosilicate glass containing less than 70% by weight of silica. Elmer et al separate the glass into a silica-rich phase and a borate-rich phase, and thereafter leach the borate phase from the glass to produce a porous silica-rich body having a pore size in the range of about 10 to 25 angstroms. The leaching solution traps moisture in the fine pores of the leached glass, which expands the glass when heated to a temperature of 1300.degree. to 1425.degree. C. by flash-firing. The porous glass particles simultaneously sinter and foam. The foam glass composition made by the method of Elmer et al suffers from the disadvantage that high firing temperatures are required and flash-firing requires a refractory-lined furnace which consumes large amounts of energy. Additionally, residual moisture is left in the final foam glass product, which increases thermal conductivity.
U.S. Pat. No. 3,945,816 to Johnson produces a foam glass from borosilicate glass having a silica content of 40 to 90% by weight, a boric oxide content of about 10 to 50% by weight, and a metal oxide flux content from about 3 to 20% by weight. The process is conducted by forming a glass comprising the above constituents, melting the materials, fritting by rapid cooling, and crushing to fine particle size. The crushed glass is then mixed with a foaming agent disclosed as alkali and alkaline earth metal carbonates. The mixture is placed in a mold and fired for a period of one and one-half (11/2) hours to a temperature of between 650.degree. C. and 850.degree. C. The foamed glass is then phase-separated into a silica-rich phase and a silica-poor phase without cooling, and the phase-separated foamed glass is subjected to a leaching to remove the silica-poor phase.
U.S. Pat. No. 4,192,664 to Joshi is directed to making a foam glass body from a high silica borosilicate glass composition by preparing a pulverulent homogenous mixture from constituents comprising amorphous silica of a micron size, alkali metal oxides, such as potassium hydroxide and potassium carbonate, a boric oxide introduced as boric acid, alumina, and a cellulating agent, such as carbon black and antimony trioxide. The foregoing components are formed into a slurry and subjected to a high shear mixing. The slurry is then subjected to drying in, for example, a spray drier to remove water from the slurry and form dry agglomerates which are then introduced into a crusher. The crushed agglomerates are then placed in a mold and sintered in a furnace at a temperature between 1200.degree. and 1450.degree. C.
U.S. Pat. No. 3,874,861 to Kurz is directed to a process for producing foamed glass from amorphous mineral particles, or mineral particles capable of being rendered amorphous by heating, and which have high silica content by mixing with gas forming agents and an alkali silicate. The foamable composition disclosed by Kurz can contain, in addition to mineral powders and alkali silicate, alkali carbonates, and gas forming agents soluble in sodium silicate (e.g., sugar). The materials are mixed, and then without drying, heated to between 750.degree. and 950.degree. C. to sinter the glass and simultaneously cause foaming by the evolution of water and liberation of CO.sub.2 (from carbonates, if any). Kurz discloses the use of diatomaceous earth and fly ash as suitable mineral powders.
The Electric Power Research Institute (EPRI) has attempted to build power poles using fly ash. In a report prepared by ECP Inc., El Segundo, Ca., entitled "Development of Power Poles From Fly Ash, Phase 2", EL-1384, Research Project 851-1, Final Report, April 1980, foam glass compositions using fly ash are described. At page 5-2 parameters of the process used by the (EPRI) and some of the properties of the foam glass compositions are described. According to the (EPRI), the foam glass composition was heated to about 1050.degree. C. above this temperature the composition foamed due to the carbonates present in the fly ash. Producing a viscous foam from fly ash and waste glass was not desirable for producing power poles.
Accordingly, it is an object of the invention to make a foam glass body from diatomaceous earth, fly ash or mixtures thereof which is inexpensive.
It is another object of the invention to make a foam glass body which is of high strength and of low thermal conductivity from diatomaceous earth, fly ash or mixtures thereof.
It is a further object of the invention to provide a method for producing foam glass from diatomaceous earth, fly ash or mixtures thereof which is adaptable for making foam glass of varying physical characteristics depending on the end use.
It is an additional object of the invention to produce a foam glass body having a water impermeable glaze for use as an exterior building material.
It is yet a further object of the invention to form a foam glass which has a fused outer protective layer.
Other objects will become apparent from the detailed description of the invention which follows.